1. Field of the Invention
The present invention relates to an optical communication system for connecting communication nodes. Specifically, the present invention relates to an optical communication system (optical network system) for flexibly connecting multiple communication nodes at low cost and with high reliability by utilizing the wavelength-routing characteristics of an arrayed waveguide grating, and for sharing memories loaded in respective communication nodes at low cost. More specifically, the present invention relates to an optical communication system which enables flexible connection of communication nodes with high reliability, by utilizing the wavelength-routing characteristics used in an arrayed waveguide grating or the like.
Priority is claimed on Japanese Patent Application No. 2002-338242 filed on Nov. 21, 2002 and Japanese Patent Application No. 2003-326317 filed on Sep. 18, 2003, the contents of which are incorporated herein by reference.
2. Description of the Related Art
With the developments in computerized offices and computerized administration, a demand for sharing information between respective communication nodes (nodes), for delivering information to a specific communication node, or for distributed processing of the specific information between respective communication nodes is increasing in intranets and networks in organizations. Therefore, a method for realizing this with low cost, easily, and stably has been desired.
As a method for realizing this, as shown in FIG. 53, it is considered to annularly connect by optical fibers, shared memory which is loaded in respective communication nodes on the network, and to sequentially transmit frames loaded with communication data between these communication nodes. FIG. 53 shows a system comprising four communication nodes 5201 to 5204. Communication modules 5012 loaded with optical transceivers and shared memories, are installed in the communication nodes 5201 to 5204, and the flow of frames F1 to F4 loaded with the respective data of the communication nodes 5201 to 5204, forms a logical ring topology. The frames F1 to F4 loaded with the respective data of the communication nodes 5201 to 5204, circulate the logical ring topology so that the data is shared between the communication nodes (for example, refer to “optical channel-enabled PMC card”, <URL: http://avaldata.com/avaldata/product/module_product/giga/apm425/apm425.html>)
Here, as a method for configuring a network by connecting communication nodes, as shown in FIG. 54A to FIG. 54B, there is so called a ring-shaped network system which physically and annularly connects respective communication nodes, represented by a token ring (for example, refer to “IEEE 802.5 Documents, 802.5c-1991(R1997) Supplement to IEEE Std 802.5-1989”, especially, chapter 2, <URL: http://www.8025.org/documents/>). In FIG. 54A, reference symbols 13001 to 1300n denote nodes.
Regarding the token ring scheme shown in FIG. 54A and FIG. 54B, by only arranging a transmission/reception circuit (transceiver) in respective communication nodes, and simply chain connecting sequentially all the communication nodes by an optical waveguide such as an optical fiber, it is possible to connect many communication nodes by transmission processing, with low cost. Therefore, it is suitable as a network which can be configured easily.
According to this scheme, as shown in FIG. 53, it is possible to share data of the memories, which all the connected communication nodes have, so that delivering, circulating, and distributed processing of signals between all the communication nodes becomes feasible.
However, in the abovementioned scheme, the problem is such that, in the case where any fault such as disconnection of an optical fiber or failure of a communication node occurs, all the other connected communication nodes are affected. That is to say, in the case where a fault occurs, the communication node that detected the fault outputs a fault signal, the respective communication nodes temporarily withdraw from the network to which they belong, and attempt automatic diagnosis in order to reconfigure the network around the faulty area. When they attempt automatic diagnosis, all the other communication nodes connected to the network are affected, and communication disconnection occurs. Furthermore, another problem is such that, in the case where a communication node is to be added to the same ring, the overall network must be paused.
Hence, in a ring-shaped network, a method for avoiding the influence of a communication fault by using a reverse route is used. For example, there is an FDDI (Fiber Distributed Data Interface) as a token ring optical communication system which duplicates a ring network by an optical fiber. In the FDDI, when a fault occurs, the reverse route can be realized by using a redundant optical fiber. However, not only is there a problem in that the fault avoiding system becomes extremely large scale, but also a redundant configuration of the transmission optical fiber is indispensable. Moreover, a token ring does not function as a shared memory network unless the ring is completed. Therefore, a convenient and stable optical communication system alternative has been desired.
Furthermore, even if the redundant configuration is employed, if a communication faults occur at more than one communication node, it becomes impossible to form a logical ring topology. Therefore, there is the drawback in that communication nodes where no fault has occurred are isolated.
Moreover, it is also considered to share the memory which the respective communication nodes accommodated in a ring network have. However, due to the abovementioned problems, there is a need for a highly reliable optical communication system as an alternative to this.